1. Field of the Invention
The present invention relates to a method of processing a resist onto a substrate such that a photoresist is coated with a substrate such as a semiconductor wafer and then the coated photoresist is exposed and developed, and to a resist processing apparatus.
2. Discussion of the Background
As the density of electric devices mounted on a substrate has been rapidly raised, the photolithography technology has been improved energetically. For example, a process for manufacturing 64 MDRAM or 256 MDRAM has been performed such that a chemically amplified resist is used in place of the conventional novolac system photoresist.
If the chemically amplified resist is exposed to light, acid generated from the sensitive material is diffused due to heating process to act on a catalyst, thus causing base resin to be decomposed or causing the molecular structure of the base resin to be changed. It leads to a fact that the base resin is made to be soluble or insoluble with respect to the developer.
Since one molecule of the catalyst of the chemically amplified resist contributes to a plurality of chemical reactions, higher photosensitivity is realized as compared with conventional resists. Moreover, the chemically amplified resist, having a high light transmittance in a short wavelength region, is able to relax the light intensity distribution in the direction of the thickness of the film even if an eximer laser beam having a short exposing wavelength is used. Thus, line widths of a level of 0.3 mm can be realized when a circuit pattern is formed.
However, the chemically amplified resist, depending on the environment by a degree greater than the conventional resists, has a risk that organic amine, such as ammonia and NMP (N-methyl.2 pyrrolidinone), and their polar materials (hereinafter simply called as "alkaline components"), each existing in the processing atmosphere in a small quantity, and the chemically amplified resist cause neutralization reactions to take place and thus the resist is devitalized. If the resist is devitalized, accurate line widths of a highly-integrated circuit pattern cannot be realized in the developing process. Thus, a so-called defective resolution takes place.
The inventors of the present invention have developed and researched the foregoing problem, thus resulting in consideration being performed such that the following three facts relate to the alkaline component which is mixed in the processing atmosphere. First, use of a solution containing ammonia as washing liquid for removing particles allowed to adhere to non-processed wafer causes alkaline component to be generated in the processing atmosphere. A second fact is such that use of hexamethyldisilazane (HMDS) in the adhesion process which is performed before the resist is applied causes the alkaline component to be generated in the processing atmosphere. A third fact is that a process for forming a reflection preventive film on the surface of the wafer by using amine solvent results in the alkaline component being generated in the processing atmosphere.
In U.S. Pat. No. 5,434,644, a resist processing apparatus has been disclosed which comprises a special chemical filter capable of removing alkaline component in the resist processing atmosphere. The element of the chemical filter is impregnated with acid components, such as phosphoric acid, so as to remove the alkaline component attributable to the neutralizing reaction with the acid component so that clean downflow air is introduced into a processing portion. If the foregoing apparatus is used for a long time, and thus the filter element deteriorates causing the removal performance also deteriorates, the filter element must be changed at proper timing because the concentration of the alkaline component in the processing atmosphere is raised gradually.
Hitherto, an operator of the apparatus samples each point of the internal atmosphere in each apparatus. Then, the concentration of the alkaline component included in each sample is analyzed. In accordance with a result of the analysis, the filter element is changed. However, the conventional method takes an excessively long time to obtain the result of the detection of the alkali concentration. Thus, a quick countermeasure against the rise in the concentration of the alkaline component in the processing atmosphere cannot be taken. Therefore, the manufacturing yield cannot be improved and the reliability of the apparatus has been unsatisfactory.